As the ophthalmic lens industry has grown, it has become desirable to supply contact lenses that are periodically and frequently replaced to minimize the possibility of user induced contamination. This has produced an opportunity for manufacturers to strive for automated methods and apparatus that are able to automatically produce high quality ophthalmic lenses in a cost-effective and highly efficient manner.
It is current practice in the art of making ophthalmic lenses, such as soft contact lenses of the hydrogel type, to form a monomer or monomer mixture that may be polymerized in a plastic mold. Details of typical direct mold processes for forming soft hydrogel contact lenses can be found in U.S. Pat. Nos. 5,080,839, 5,039,459, 4,889,664, and 4,495,313, the entire disclosure of each of these patents being incorporated herein by this specific reference.
The process for forming soft contact lenses as generally described in the abovementioned patents includes the steps of dissolving a monomer mixture in a non-aqueous, water-displaceable solvent and placing the monomer/solvent mixture in a mold having the shape of the final desired hydrogel lens. Next, the monomer/solvent mixture is subjected to conditions whereby the monomer(s) polymerize, to thereby produce a polymer/solvent mixture in the shape of the final desired hydrogel lens. After the polymerization is complete, the solvent is displaced with water to produce a hydrated lens whose final size and shape are similar to the shape of the original molded polymer/solvent article.
Examples of typical plastic molds used for carrying the polymerizable mixture are disclosed in U.S. Pat. Nos. 5,094,609, 4,565,348, 4,640,489 and 4,121,896, the entire disclosure of each of these patents being incorporated herein by this specific reference. The mold disclosed in U.S. Pat. No. 4,640,489 is a two-piece mold with a female mold portion having a generally concave lens surface, and a male mold portion having a generally convex lens surface, both mold portions preferably made of a thermoplastic material such as polystyrene. As discussed in U.S. Pat. No. 4,640,489, polystyrene and copolymers thereof is a preferred mold material because these materials do not crystallize during cooling from the melt, and exhibit little or no shrinkage when subject to the processing conditions required during the direct molding process discussed above. Alternatively, molds made of polypropylene or polyethylene, such as described in U.S. Pat. No. 4,121,896 may be used.
During the molding process, the monomer and monomer mixture is supplied in excess to the female concave mold portion prior to the mating of the molds. After the mold portions are placed together, defining the lens and forming a lens edge, the excess monomer or monomer mixture is expelled from the mold cavity and rests on or between flanges that surround one or both mold portions. Upon polymerization this excess material forms an annular ring around the formed lens between the flange portions of the molds.
As discussed in the above-mentioned U.S. Pat. Nos. 5,039,459, 4,889,664, and 4,565,348, it is important that the materials, chemistry, and processes be controlled so that the mold portions may be effectively separated without having to apply undue force, which may be necessary when the lens adheres to one or more of the lens mold portions or when the lens mold portions have become adhered to each other by the HEMA ring after polymerization.
Typical prior art processes for separating the mold portions and removing the lens therefrom consist of a heating stage, a prying stage and a lens removal stage. The heating stage of the prior art lens removal process usually involves applying heat to the back mold portion by applying a heated air stream to the mold. The differential expansion between the heated mold polymer and the cooler lens polymer shifts one surface with respect to the other. During the prying stage, a side pry bar is jammed between the molds from one side, and the back curve mold is pried to pivot the back curve mold upwardly from one side. The prying force then breaks the polymerized lens/polymer mold adhesion and separates the mold portions.
Martin et al., U.S. Pat. No. 5,935,492, which is incorporated herein in its entirety by this specific reference, discloses a method for demolding ophthalmic lenses using mechanical leverage and a predetermined pattern of motion to gradually pry lens mold sections apart from one another.
It has been recognized, such as disclosed in U.S. Pat. No. 5,850,107, which is incorporated herein in its entirety by this reference, that when there exists a temperature gradient between the mold halves and the lens, there is less an adhesion force existing between the lens and the mold surfaces. It has been suggested that this effect is most significant when there is a maximum thermal gradient between the mold halves and the lens. Generally, lower thermal gradients created between the mold halves and the lens will require a greater force to separate the mold portions resulting in increased possibility of damaging a lens or fracturing a mold portion.
Techniques have therefore been proposed that are directed toward heating a mold section to create a temperature gradient in order to facilitate the demolding process. For example, U.S. Pat. No. 5,850,107 describes a process including applying hot steam to a back curve mold half to form such a temperature gradient and prying the mold sections apart.
A conventional approach to removing a contact lens from a mold section, or mold cup, of a newly separated mold assembly, employs the use of a vacuum head. The vacuum head is placed into contact with the exposed side of the contact lens and vacuum is drawn through a single hole therein. The vacuum contacts a minor portion, that is less than 50%, of the area of the surface facing the vacuum head. Vacuum is often applied using a motorized constant vacuum machine. Using such a conventional vacuum system runs a substantial risk of damaging the contact lens and allowing liquid from or in contact with the lens to enter into the vacuum system, placing an added burden on such system.
Cameron U.S. Pat. No. 6,288,852 discloses a method and apparatus for retaining a contact lens in a fixed position to allow coloring of the lens. The mounting assembly disclosed in this patent includes a surface on which the contact lens is fixed with the assistance of a vacuum created by a vacuum pump. The vacuum passes through the mounting assembly and through a plurality of small capillaries in the surface. This patent does not disclose or suggest removing a contact lens from a molding cup.
Conventional polymeric contact lens manufacturing and processing techniques require recently formed lenses to be further processed before final packaging of the lenses. For example, newly formed contact lenses are subjected to extraction and hydration procedures using one or more fluids, for example, liquids. To illustrate, newly formed polymeric contact lenses often contain unreacted monomers which are removed by extracting the monomers from the lens with a liquid medium, such as a non-aqueous liquid medium. After the extraction processing, the contact lens is contacted with an aqueous liquid medium to hydrate the lens, for example, to swell the lens with water.
During such fluid processing, the lenses can become damaged, for example, by the fluid processing itself and/or as the lenses are moved between processing steps. In addition, since a large number of different contact lenses, for example, contact lenses having one or more of different base curves, different refractive powers, different overall diameters, different cylinder corrections, if any, and the like differences, are often processed at the same time, such lenses can be misidentified after the processing. Such misidentified lenses can result in added manufacturing costs, higher lens discard rates, and even mislabeling of the final lens product and/or providing the wrong lens to the ultimate consumer, the lens wearer.
There is still a need for more effective methods and systems for demolding contact lenses, especially silicone hydrogel contact lenses. For example, it would improve the simplicity and the efficiency of the automated production of hydrogel lenses if the demolding process included steps for reliably controlling which mold section, i.e. which one of either the male mold section or the female mold section, would contain the molded lens product upon separation of the mold sections. In addition, there is a need for apparatus and methods for facilitating removal of recently formed contact lenses from mold sections and apparatus and methods for placing such removed lenses onto holders useful for downstream lens processing steps, for example, extraction and hydration processing steps.